Method of producing milling adjuvants and/or dispersive agents, by physicochemical separation; adjuvants and agents thus obtained; and uses of the same

ABSTRACT

A method of producing milling adjuvants and/or dispersing agents, with the use of a separation apparatus which is comprised of one or more organic and/or mineral membranes; a milling adjuvant and/or dispersing agent produced by said method; and use of said adjuvant/agent in preparing an aqueous suspension of mineral particles; and the use of the aqueous suspension in applications involving pigments.

This is a Division of application Ser. No. 08/572,047 filed on Dec. 14,1995 now U.S. Pat. No. 5,954,967.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a method of producing a milling adjuvant ordispersing agent, by physicochemical separation of vinyl polymers orcopolymers, acrylic polymers or copolymers, or polycondensate polymersor copolymers, by at least one technique of extraction, filtration,ultrafiltration, nanofiltration, or reverse osmosis.

The invention also relates to a milling adjuvant or dispersing agent,resulting from one of the above-mentioned separation methods, and use ofthis adjuvant or agent in producing an aqueous suspension of mineralparticles intended for use in an application involving a pigment.

The invention further relates to an aqueous suspension of mineralparticles which contain the adjuvant or agent. In addition, theinvention relates to an application of the suspension to a pigmenttechnology, e.g. paper, paint and other coating, plastic. The inventionalso relates to a drilling technology, public works, a ceramic, andother areas.

2. Description of the Prior Art

Means of separation of polymers in solution are known to persons skilledin the art. A phase equilibration method disclosed in Cantow, M. R. J.,"Polymer fractionation", Academic Press,, N.Y.C. (1967), describes theseparation of polymers according to molecular weight or chemicalcomposition but does not enable production of an adjuvant specificallyuseful for milling or an agent specifically useful for dispersion of apulverulent material, and does not employ a membrane.

Other references such as Fr. Pat. 2,488,814 and Eur. Pats. 0,127,388 and0,542,643, or Eur. Pat. 0,499,267 describe a method of separating awater-soluble acrylic polymer or copolymer of different molecularweights, with the aim of producing a milling adjuvant or dispersingagent for pulverulent mineral particles in an aqueous suspension, foruse in an application involving a pigment.

These methods, based on differences in solubility of polymers ofdifferent molecular weights in a solution containing a polar solventsuch as isopropanol, are hazardous to employ and are increasinglysubject to legal restrictions. Furthermore, these methods do not allowseparation of acrylic polymers or copolymers in a fully acidic state.

An advantage of separation of acrylic polymers or copolymers in thefully acidic state is that it allows any of a wide range of neutralizingagents to be employed in neutralizing the fractions employed in a givenapplication.

Historically, numerous approaches have been made to exploit differencesin solubility for purposes of separation, but even those which give goodseparation results have not been entirely satisfactory. The presentapplicant did not believe that the state of the art methods were subjectto appreciable further improvement.

SUMMARY OF THE INVENTION

The applicant investigated a radically different approach, which has ledto development of a separation method, usable in either a continuous orbatch process, wherein one may optionally operate with no organicsolvent, or with an immiscible solvent, and wherein one has broad choiceof certain other parameters such as

neutralization of acid groups in the polymer(s) or copolymer(s),

concentration of the medium,

temperature,

optionally polarity of the solvent,

optionally type of any purely organic solvent used.

This object and other objects as will be better understood from thefollowing description have been obtained by a milling adjuvant ordispersing agent comprising the steps of:

subjecting a water-soluble separand material into a physicochemicalseparation, said water-soluble separand material being selected from thegroup consisting of a vinyl polymer, a vinyl copolymer, an acrylicpolymer, an acrylic copolymer, a polycondensate polymer and apolycondensate copolymer, by a technique of extraction, filtration,ultra filtration, nanofiltration or reverse osmosis, in a continuous orbatch process, employing a separation apparatus, said apparatuscomprising at least one organic or mineral membrane, said membrane beingoptionally borne on a support, wherein said water-soluble separandmaterial has at least one acidic functional group;

separating said water-soluble separand into useful phases at least oneof said phases corresponding to a milling adjuvant or dispersing agent.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The described method enables one to produce, surprisingly, awater-soluble milling adjuvant or dispersing agent which facilitates theproduction of an aqueous suspension of mineral particles intended foruse in an application involving a pigment.

Another object of the present invention is the production, by means ofthe method of the invention, of a water-soluble milling adjuvant ordispersing agent which facilitates the production of an aqueoussuspension of mineral particles intended for use in an applicationinvolving a pigment.

A further object of the invention is an aqueous suspension of mineralparticles produced with the aid of the adjuvant or agent of the presentinvention; applications of such a suspension in the areas of atechnology of: paper, paint and coating, plastic, ceramic, watertreatment, drilling (such as use in muds), treatment of a synthetictextile, or any other application requiring the use of an aqueoussuspension of mineral particles.

These objects are achieved by means of the inventive method ofseparation, into fractions, of a vinyl polymer or copolymer, an acrylicpolymer or copolymer, or a polycondensate polymer or copolymer, by atechnique of extraction, filtration, ultrafiltration, nanofiltration, orreverse osmosis, in an aqueous medium, an aqueous alcoholic medium, or asolvent medium.

Whereas the state of the art employs a technique of separating variousfractions based on differences in partition coefficient of the fractions(resulting in differences in solubilities), the inventive methodaccording to the present invention is distinguished in that it is basedon the differences in hydrodynamic volume and (in some cases) on theinteraction between a membrane and separand.

The term "hydrodynamic volume" is understood to mean the volume occupiedby polymer molecules as a function of various physicochemical parametersof the medium which affect the passage of polymer chains through amembrane, and as a function of possible chemical treatment of amembrane, which treatment would be of a type which one skilled in theart would deem capable of influencing the separation conditions.

The inventive method enables a continuous or batch process of separationinto various phases to be carried out in which a separand is in thefully acidic state, or partially neutralized, or fully neutralized, andwhich does not require a third solvent (either polar or non-polar).

The method of the invention of producing a milling adjuvant ordispersing agent, by physicochemical separation of a vinyl polymer or acopolymer, an acrylic polymer or a copolymer, a polycondensate polymeror a copolymer, by a technique of extraction, filtration,ultrafiltration, nanofiltration, or reverse osmosis, of a water-solubleseparand, is characterized in that: it makes use of a separationapparatus comprising one or more organic or mineral membranes, whichmembranes may be borne on a support, whereby the said water-solubleseparand is separated into various useful phases at least one of whichphases corresponds to a milling adjuvant or a dispersing agent forproducing an aqueous suspension of mineral particles intended for use inan application involving a pigment.

The term "useful phases" used here is understood to signify that phasesnot used as a milling adjuvant or dispersing agent may be usable inrelated or other technologies.

The described apparatus, comprised of

at least one membrane, which may have any of various geometricconfigurations (e.g. conical or cylindrical), and

optionally at least one support, which may have a geometric shape(s)identical to or different from that of the membrane, and has pores,which may be symmetric or asymmetric. The membrane, which may be treatedby an organic or mineral agent, may be of a type characterized ascapillary, or conduit-shaped, or nozzle shaped, or spiral, having adiameter or a distance apart which may vary; or it may be configured asa flat surface, wherein the distance between a surface with anothersurface may vary. The membranes may be organized in parallel or inseries, and may be subjected to constant or intermittent ultrasonicwaves for purposes of unblocking them.

The inventive milling adjuvant or dispersing agent, obtained by theinventive separation method, is purified, and is characterized by amolecular weight distribution curve obtained by aqueous GPC (gelpermeation chromatography) with refractometric detection, wherein, inthe curve, the second inflection peak, corresponding to a shoulder, hasan attenuation, with respect to the initial product, of at least, 3% andpreferably at least 10%.

Further, the inventive milling adjuvant or dispersing agent, obtained bythe inventive separation method, is characterized in that the groupsgenerating the acid function contained in the adjuvant or agent arepartially or completely neutralized by one or more monovalent orpolyvalent neutralizing agent, such as, in particular, sodium hydroxide,potassium hydroxide, ammonium hydroxide, lithium hydroxide, zinchydroxide, calcium hydroxide, magnesium hydroxide, aluminum hydroxide,or a primary, secondary, or tertiary aliphatic amine, or a primary,secondary, or tertiary cyclic amine.

The aqueous suspension of mineral particles is characterized in that itcontains 0.05-2% of one or more milling adjuvant or dispersing agentaccording to the invention.

The fraction of the water-soluble vinyl polymer or copolymer, acrylicpolymer or copolymer, or polycondensate polymer or copolymer, whichpolymeric material is intended to be used as a milling adjuvant ordispersing agent to produce a suspension for use in a pigmenttechnology, is generally obtained by separation from thepolymer-containing solution obtained by a known method ofpolycondensation or radical polymerization, which method has beencarried out in the presence of:

a polymerization regulator such as, e.g., an organic compound based on areducing moiety such as, in particular, a hydroxylamine, and

a polymerization initiator such as a peroxide or a persalt, e.g.hydrogen peroxide, sodium persulfate, sodium hypophosphite, orhypophosphorous acid.

A monomer or comonomer employed is one or more of the following:

the following acids: (meth)acrylic, itaconic, crotonic, fumaric,isocrotonic, aconitic, mesaconic, sinapic, undecylenic, angelic,canellic, hydroxyacrylic, or maleic anhydride; these acids being used inthe acid form or partially or completely neutralized;

cationic monomers, e.g. the following: dimethylaminoethyl(meth)acrylate, dimethyl diallylammonium chloride,1-(methacrylamido)propyl-3-trimethylammonium chloride, and derivativesand mixtures of these;

sulfone-type or sulfonate-type comonomers, of the type ofacrylamidomethyl propyl sulfone or methallyl sulfonate; and

comonomers such as: acrolein, acrylamide, acrylonitrile, esters of(meth)acrylic acid, vinylpyrrolidone, vinylcaprolactam, ethylene,propylene, isobutylene, diisobutylene, vinyl acetate, styrene,α-methylstyrene, and methyl vinyl ketone;

the polymerization medium may comprise water, methanol, ethanol,propanol, isopropanol, a butanol or mixture of butanols,dimethylformamide, dimethyl sulfoxide, tetrahydrofuran, acetone, methylethyl ketone, ethyl acetate, butyl acetate, hexane, heptane, benzene,toluene, xylene, mercaptoethanol, tertdodecyl mercaptan, acetic acid,tartaric acid, lactic acid, citric acid, gluconic acid, glucoheptonicacid, 2-mercaptopropanoic acid, di-2-hydroxyethyl sulfide, halogenatedsolvents e.g. carbon tetrachloride, chloroform, or dichloromethane, andethers of monopropylene glycol or of diethylene glycol, and mixtures ofsuch ethers.

In the polymer solution being subjected to separation, the moietiesgenerating an acid function on the polymers are in the acid state orpartially neutralized. The neutralization (or further neutralization)may be affected by one or more monovalent or polyvalent neutralizationagents, such as, in particular, sodium hydroxide, potassium hydroxide,ammonium hydroxide, lithium hydroxide, zinc hydroxide, calciumhydroxide, magnesium hydroxide, aluminum hydroxide, or a primary,secondary, or tertiary aliphatic amine, or a primary, secondary, ortertiary cyclic amine, etc., and possibly followed by distillation toremove a solvent other than water in the polymerization medium.

The polymer solution, which may or may not be aqueous and may or may nothave undergone distillation, is then introduced into a vessel which maybe equipped with means of thorough intermixing. The initial dry matterconcentration of the solution subjected to mixing may be on the order of20-500%, or the concentration of the dry matter may be reduced to1.5-20% by dilution with water. The solution is then pumped to aseparation system such as ultrafiltration, nanofiltration, or reverseosmosis, with or without back pressure in one or more passages, and withor without recycling. Temperatures in the separation system may be ashigh as 70° C. or even 150° C.

The configuration of the membrane used may be, e.g., flat, helical,capillary, or tubular, with a single module or a combination of aplurality of modules, which may or may not be isolated, and may bearranged in parallel or in series.

The membrane may be supported by a support having a matching ordifferent configuration, and further the membrane may have its surfacetreated by various additives such as, e.g., polyphosphazene, quaternarypolyvinylimidazole, quaternary polyethylene, Naflon, Solgel, or others.

The membrane is chosen so as to be capable of separating the polymersolution, in which the polymer is in the fully acidic state, orpartially neutralized, or fully neutralized state, into various usefulfractions one of which comprises the milling adjuvant or dispersingagent according to the invention for producing an aqueous suspension ofmineral particles intended for use in a pigment technology.

The apparatus enables the inventive method to be carried out and alsoenables recovery of one of the fractions, e.g. the retentate, to berecycled to the initial vessel or to be mixed with the polymer for oneor more additional passages through the separation apparatus.

A plurality of membranes of the same or different type may be employed.All of the phases produced may be recovered and employed as usefulfractions.

The retentate corresponding to the inventive adjuvant or agent ispurified and is characterized by a molecular weight distribution curveobtained by aqueous GPC (gel permeation chromatography) withrefractometric detection, wherein, in the curve, the second inflectionpeak (corresponding to a shoulder) has an attenuation, with respect tothe initial product, of at least 3% and preferably at least about 10%.

The phase containing the fraction of polymers or copolymerscorresponding to the adjuvant or agent according to the invention may beemployed in the form obtained as a liquid in solution, for use as amilling adjuvant for a mineral substance to be processed; or theabove-mentioned phase may be subjected to any known means for isolatingthe vinyl polymers or copolymers, acrylic polymers or copolymers, orpolycondensate polymers or copolymers, in the form of a fine powderwhich can be employed as a milling adjuvant.

In practice, the fine milling (fine comminution) of a mineral substanceconsists of grinding the mineral substance with a milling material toform very fine particles in an aqueous medium containing the millingadjuvant.

The substance to be milled is placed in an aqueous suspension. A millingmaterial is added to the suspension, which milling materialadvantageously has a particle size distribution in the range 0.2-4.0 mm.The milling material is generally present in the form of particles ofvarious types selected from a wide range of materials such as silicondioxide, aluminum oxide, zirconium oxide, or mixtures of these, or ahard synthetic resin, steel, etc. An example of a composition of amilling material is disclosed in Fr. Pat 2,203,681:

    ______________________________________                                        zirconium oxide      30-70 wt. %                                              aluminum oxide       0.1-5 wt. %                                              silicon dioxide      5-20 wt. %.                                              ______________________________________                                    

Preferably, the milling material is added to the suspension in an amountsuch that its ratio (by weight) to the mineral substance to be milled isat least 2:1, and preferably is in the range 3:1 to 5:1.

The mixture of the suspension and the milling material is then subjectedto mechanical agitation, of the type produced in a classical mill havingmicroelements.

The milling adjuvant or dispersing agent of the invention is introducedto the mixture formed by the aqueous suspension of a mineral material tobe milled and the milling material, in an amount of 0.05-2 wt. % of theadjuvant (based on the dry weight of the polymer comprising theadjuvant, and based on the dry weight of the mineral materials to bemilled).

The time needed to achieve the desired fineness of the mineralsubstances being milled varies depending on the nature and quantity ofthe substances, and further depending on the means of agitation employedand the temperature of the medium during the milling.

The mineral substances to be milled may be of widely varying origins.E.g. they may comprise (natural or synthetic) calcium carbonate,dolomite, calcium sulfate, titanium dioxide, aluminum hydroxide, orsilicates and aluminosilicates (e.g. kaolin, mica, talc, or bentonite);in general, they may comprise any mineral substances which requiremilling in order to be usable in a wide variety of applications such ascoating of paper, pigmenting of paints and other coatings, filling ofrubbers or synthetic resins, treating of synthetic textiles, treating ofwater, formulating of drilling muds, etc.

The use of the inventive milling adjuvant or dispersing agentfacilitates the milling of a mineral material having a relatively largeparticle size, in aqueous suspension with a high concentration of drymatter, to produce a mineral material having a relatively fine particlesize.

This application is based on the French application Fr. 94-15440 whichis incorporated herewith by reference.

Having generally described this invention, a further understanding canbe obtained by reference to certain specific examples which are providedherein for the purpose of illustration only and are not intended to belimiting unless otherwise specified.

EXAMPLES Example 1

A milling adjuvant or dispersing agent according to the invention wasobtained by separation of a sodium polyacrylate completely neutralizedby sodium hydroxide. The separation employed a capillary membrane andwas carried out at about 25° C. using various concentrations of drymatter. The product was then used as a milling adjuvant or dispersingagent.

Experiment No. 1:

An aqueous solution containing 32% of completely neutralized sodiumpolyacrylate with weight average molecular weight Mw=6000 (determined byaqueous GPC, using a standard comprising a series of sodiumpolyacrylates supplied by the firm Polymer Standards Service under thename "PSS-PAA", of molecular weights 2000 to 8000) was introduced to theseparating apparatus by means of a pump delivering 144 L/hr. Theapparatus employed a "UFP-5-E-6A" capillary membrane containing 170capillaries, supplied by the firm Sempas.

After 6 hr of operation of the apparatus at a feed rate of 144 L/hr anda temperature of 24.3-25.1° C., entrance pressure 480-540 kPa, and exitpressure 20-100 kPa, the retentate., corresponding to a milling adjuvantor dispersing agent according to the invention, was a completelyneutralized sodium polyacrylate in water at a concentration of 31.5%based on dry matter, the polyacrylate having weight average molecularweight Mw=6250 (by aqueous GPC), and was characterized by a molecularweight distribution curve obtained by aqueous GPC with refractometricdetection, wherein, in the curve, the second inflection peak had anattenuation, with respect to the initial product, of 3.8%; and thepermeate was a completely neutralized sodium polyacrylate having aweight average molecular weight Mw=3200 (by aqueous GPC), in water at aconcentration of 29.2% based on dry matter.

Experiment No. 2:

The same apparatus was used as in Experiment No. 1, and the samepolyacrylate was fed, but diluted to a concentration of 10% (using waterpurified by reverse osmosis for the dilution).

The same standards were used for the GPC determination as were used inExample 1.

After 2 hr of operation of the apparatus at a feed rate of 950 L/hr anda temperature which increased progressively from 18.5 to 27.7° C., withentrance pressure which increased from 270 to 290 kPa, and exit pressurefrom 100 to 110 kPa, the retentate, corresponding to a milling adjuvantor dispersing agent according to the invention, was a completelyneutralized sodium polyacrylate having a weight average molecular weightMw=6400 (by aqueous GPC), in water at a concentration of 10.2% based ondry matter, and was characterized by a molecular weight distributioncurve obtained by aqueous GPC with refractometric detection, wherein, inthe curve, the second inflection peak, corresponding to a shoulder, hadan attenuation, with respect to the initial product, of 17.4%; and thepermeate was a completely neutralized sodium polyacrylate having aweight average molecular weight Mw=3000 (by aqueous GPC), in water at aconcentration of 7.5% based an dry matter).

Experiment No. 3:

The same apparatus was used as in Experiment No. 1, and the samepolyacrylate was fed, but diluted to a concentration of 5% (using waterpurified by reverse osmosis for the dilution).

The same standards were used for the GPC determination as were used inExample 1.

After 5 hr of operation of the apparatus at a feed rate of 950 L/hr anda temperature which increased progressively from 17.7 to 27.7° C., withentrance pressure which changed from 270 to 200 kPa, and exit pressurefrom 110 to 90 kPa, the retentate, corresponding to a milling adjuvantor dispersing agent according to the invention, was a completelyneutralized sodium polyacrylate having a weight average molecular weightMw=6500 (by aqueous GPC), in water at a concentration of 6.1% based ondry matter, and was characterized by a molecular weight distributioncurve obtained by aqueous GPC with refractometric detection, where, inthe curve, the second inflection peak, corresponding to a shoulder, hadan attenuation, with respect to the initial product, of 13%; and thepermeate was a completely neutralized sodium polyacrylate having aweight average molecular weight Mw=2000 (by aqueous GPC), in water at aconcentration of 3.0% based on dry matter.

Experiments Nos. 4 to 7:

In each of these experiments, a suspension of calcium carbonate of largeparticle size was subjected to milling to produce a suspension of fineparticle size.

The suspension of the coarse material was prepared from a naturalcalcium carbonate, using the following:

For Experiment No. 4, illustrating the prior art, a completelyneutralized sodium polyacrylate of weight average molecular weightMw=6000 (by aqueous GPC), in water at a concentration of 32% based ondry matter, resulting from radical polymerization of acrylic acid, andcorresponding to the product fed to the separating apparatus;

For Experiment No. 5, illustrating the invention, the completelyneutralized sodium polyacrylate from Experiment No. 1, having Mw=6250;

For Experiment No. 6, illustrating the invention, the completelyneutralized sodium polyacrylate from Experiment No. 2, having Mw=6400;

For Experiment No. 7, illustrating the invention, the completelyneutralized sodium polyacrylate from Experiment No. 3, having Mw=6500.

For each of these experiments, an aqueous suspension of calciumcarbonate from the Orgon deposit, in France, was prepared. The particlesize of this material was less than 10 microns, and the dry mattercontent of the aqueous suspension was 76 wt. % based on the total weightof the suspension.

The milling adjuvant was introduced into the suspension in amountsindicated in the Table, infra, given in units of wt. % dry matter, basedon the dry weight of the calcium carbonate to be milled.

The suspension was circulated in a "Dyno-Mill" mill having a fixedcylinder and a rotating impeller, with the milling material comprisingspheres of corundum of diameter in the range 0.6-1.0 mm.

The total volume occupied by the milling material was 1150 cc, and itsweight was 2900 g. The milling chamber had volume 1400 cc. Thecircumferential speed of the mill was 10 m/sec. The calcium carbonatesuspension was recycled at a rate of 18 L/hr.

The output of the Dyno-Mill was equipped with a 200 micron screenseparator, to provide means of separating the milling material from thefinal suspension.

The temperature of the experiments was maintained at about 60° C. duringthe milling.

At the end of the milling process (time T₀), a sample of the pigmentsuspension with 80% of the particles having particle size less than 1micron was collected in a flask, and the viscosity of the suspension wasmeasured with a type RVT Brookfield viscometer, at 20° C. and rotationalspeeds of 10 and 100 rpm with an adequate spindle.

After the suspension was allowed to rest 8 days in the flask, a suitablespindle for the type RVT Brookfield viscometer was introduced into theflask, which had not been agitated, and the viscosity was measured at20° C. and speeds 10 and 100 rpm (code "AVAG"=before agitation).

The viscosity was again measured after agitation of the flask, toprovide a value after agitation (code "APAG").

The experimental results are presented in Table 1.

It is seen from Table 1 that, independently of the dry matterconcentration of the polymer to be fractionated, the separation with theaid of a capillary membrane enables one to obtain a milling adjuvant ordispersing agent according to the invention which adjuvant or agent hasa molecular weight distribution curve obtained by aqueous GPC withrefractometric detection, where, in the curve, the second inflectionpeak, corresponding to a shoulder, has an attenuation, with respect tothe initial product, of at least 3.8%.

                                      TABLE 1                                     __________________________________________________________________________             Milling Adjuvant Used                                                         Neutrali-                                                                             Atten-    Consumption                                                                         Brookfield Viscosity of the Suspension                zation  uatin in  of milling                                                                          (mPa-sec), at 20° C. and 76% dry                                       matter                                                for     second    adjuvant (%       8 days                                                                            8 days                                                                            8 days                   Experi-  Separation                                                                            inflection                                                                          Dry on dry    T.sub.0                                                                           8 days                                                                            AVAG                                                                              APAG,                                                                             APAG                     ment     (% and  peak of GPC                                                                         Matter                                                                            matter                                                                              T.sub.0 and                                                                       100 AVAG,                                                                             100 at 10                                                                             100                      No.      ion used)                                                                          Mw curve (%)                                                                           (%) basis)                                                                              10 rpm                                                                            T/min                                                                             10 rpm                                                                            T/min                                                                             rpm T/min                    __________________________________________________________________________    Prior Art                                                                          4   100 Na                                                                             6000                                                                             0     32  0.95  2000                                                                              640 33800                                                                             4500                                                                              15700                                                                             3230                     Invention                                                                          5   100 Na                                                                             6250                                                                             3.8   31.5                                                                              0.82   650                                                                              230  6150                                                                              500                                                                              1250                                                                               250                     Invention                                                                          6   100 Na                                                                             6400                                                                             17.4  10.2                                                                              0.94  2000                                                                              770 23400                                                                             4100                                                                              7650                                                                              1930                     Invention                                                                          7   100 Na                                                                             6500                                                                             13.0  6.1 0.92  1530                                                                              520 25480                                                                             3800                                                                              6560                                                                              1600                     __________________________________________________________________________     AVAG: Measure of the viscosity prior to agitation of the suspension           APAG: Measure of the viscosity after agitation                           

It is also seen from Table 1 that the milling adjuvant or dispersingagent according to the invention enables production -of an aqueoussuspension of calcium carbonate which is highly concentrated and whichnonetheless has a Brookfield viscosity which is lower than that of priorart suspensions, at an adequate speed of rotation of the spindle, namelyon the order of 10 rpm, after 8 days without agitation. In practice,this result translates into improved pumpability of the suspension afterbeing stored several days in a non-agitated vessel.

Example 2

In this Example, a milling adjuvant or dispersing agent according to theinvention was obtained by separation of a mixed sodium and calciumpolyacrylate completely neutralized by sodium hydroxide and calciumhydroxide. The separation employed a capillary membrane and was carriedout at a temperature varying from 17 to 28° C. The product was then usedas a milling adjuvant or dispersing agent.

Experiment No. 8:

An aqueous solution containing 32% of polyacrylate completelyneutralized by a mixture comprised of 76% sodium hydroxide and 24%calcium hydroxide, the polyacrylate having a weight average molecularweight Mw=6000 (determined by aqueous GPC), was diluted to 10% usingwater purified by reverse osmosis, and was then subjected to separationon the same apparatus as in Experiment No. 1, under the conditionsdescribed below.

The same standards were used for the GPC determination as were used inExample 1.

After 2 hr of operation of the apparatus at a feed rate of 1000 L/hr anda temperature which increased progressively from 17 to 28° C., withentrance pressure which decreased from 280 to 260 kPa (meanwhile passingthrough a maximum of 300 kPa), and exit pressure increasing from 100 to120 kPa, the retentate, corresponding to a milling adjuvant ordispersing agent according to the invention, was a completelyneutralized sodium-calcium (mixed) polyacrylate having a weight averagemolecular weight Mw=6200 (by aqueous GPC), in water at a concentrationof 10.6% based on dry matter, and was characterized by a molecularweight distribution curve obtained by aqueous GPC with refractometricdetection, wherein (in the curve) the second inflection peak(corresponding to a shoulder) had an attenuation, with respect to theinitial product, of 3.8%; and the permeate was a completely neutralizedsodium-calcium (mixed) polyacrylate having a weight average molecularweight Mw=1570 (by aqueous GPC), in water at a concentration of 5.1%based on dry matter.

Experiments Nos. 9 comparison and 10:

In these Experiments, a suspension of calcium carbonate of relativelylarge particle size was subjected to milling to produce a suspension ofmicroparticles.

The suspension of calcium carbonate of relatively large particle sizewas prepared from a calcium carbonate, using the following:

For Experiment No. 9, illustrating the prior art, a completelyneutralized sodium-calcium (mixed) polyacrylate having a weight averagemolecular weight Mw=6000 (by aqueous GPC), resulting from radicalpolymerization of acrylic acid and corresponding to the material fed tothe separation apparatus;

For Experiment No. 10, illustrating the invention, the completelyneutralized sodium-calcium (mixed) polyacrylate of Experiment No. 8,having a weight average molecular weight Mw=6200.

For Experiments Nos. 9 and 10, the aqueous suspension of calciumcarbonate was prepared and milled with the same apparatus and under thesame operating conditions as in Experiments Nos. 4-7.

The experimental results are presented in Table 2.

It is seen from Table 2 that the separation, with the aid of a capillarymembrane, of the fractions of the polyacrylate completely neutralized bya mixture of sodium hydroxide and calcium hydroxide enables one toobtain a milling adjuvant or dispersing agent according to the inventionwhich adjuvant or agent has a molecular weight distribution curveobtained by aqueous GPC with refractometric detection, wherein (in thecurve) the second inflection peak, corresponding to a shoulder, has anattenuation, with respect to the initial product, of at least 3.8%.

                                      TABLE 2                                     __________________________________________________________________________             Milling Adjuvant Used                                                         Neutrali-                                                                              Atten-    Consumption                                                                         Brookfield Viscosity of the Suspension               zation   uatin in  of milling                                                                          (mPa-sec), at 20° C. and 76% dry                                       matter                                               for      second    adjuvant (%       8 days                                                                            8 days                                                                            8 days                  Experi-  Separation                                                                             inflection                                                                          Dry on dry    T.sub.0                                                                           8 days                                                                            AVAG                                                                              APAG,                                                                             APAG                    ment     (% and   peak of GPC                                                                         Matter                                                                            matter                                                                              T.sub.0 and                                                                       100 AVAG,                                                                             100 at 10                                                                             100                     No.      ion used)                                                                           Mw curve (%)                                                                           (%) basis)                                                                              10 rpm                                                                            T/min                                                                             10 rpm                                                                            T/min                                                                             rpm T/min                   __________________________________________________________________________    Prior Art                                                                           9  76 Na/24 Ca                                                                         6000                                                                             0     32  1.05  1300                                                                              430 5710                                                                              1100                                                                              1100                                                                              360                     Invention                                                                          10  76 Na/24 Ca                                                                         6200                                                                             3.8   10.6                                                                              1.05  1300                                                                              420 3730                                                                               980                                                                              1100                                                                              360                     __________________________________________________________________________     AVAG: Measure of the viscosity prior to agitation of the suspension           APAG: Measure of the viscosity after agitation                           

It is also seen from Table 2 that the inventive milling adjuvant ordispersing agent according to the invention enables production of anaqueous suspension of calcium carbonate which is highly concentrated andwhich, nonetheless, has a Brookfield viscosity which is lower than thatof prior art suspensions, at an adequate speed of rotation of thespindle, namely in the order of 10 rpm, after 8 days without agitation.In practice, this result translates into improved pumpability of thesuspension after being stored several days in a non-agitated vessel.

Example 3

In this Example, a milling adjuvant or dispersing agent according to theinvention was obtained by separation of a sodium polyacrylate partiallyneutralized (to the extent of 50%) by sodium hydroxide. The separationemployed a capillary membrane and was carried out at a temperaturevarying from 18 to 28° C. The product was then used as a millingadjuvant or dispersing agent.

Experiment No. 11:

An aqueous solution containing 29% of polyacrylate partially neutralized(to the extent of 50%) by sodium hydroxide, the above polyacrylatehaving a weight average molecular weight Mw=6000 (determined by aqueousGPC), was diluted to 10 using water purified by reverse osmosis, and wasthen subjected to separation on the same apparatus as in Experiment No.1, under the conditions described below.

The same standards were used for the GPC determination as were used inExample 1.

After 2 hr of operation of the apparatus at a feed rate of 1000 L/hr anda temperature which increased progressively from 18 to 28° C., withentrance pressure which decreased from 310 to 300 kPa (meanwhile passingthrough a maximum of 320 kPa), and exit pressure increasing from 100 to110 kPa, the retentate, corresponding to a milling adjuvant ordispersing agent according to the invention, was a sodium polyacrylate,partially neutralized (to the extent of 50%), having a weight averagemolecular weight Mw=6070 (by aqueous GPC), in water at a concentrationof 10.1% based on dry matter, and was characterized by a molecularweight distribution curve obtained by aqueous GPC with refractometricdetection, wherein (in the curve) the second inflection peak(corresponding to a shoulder) had an attenuation, with respect to theinitial product, of 9.9%; and the permeate was a sodium polyacrylate,partially neutralized (to the extent of 50%), having a weight averagemolecular weight Mw=2500 (by aqueous GPC), in water at a concentrationof 6.9% based on dry matter.

Experiments Nos. 12 (comparative) and 13:

In these Experiments, a suspension of calcium carbonate of relativelylarge particle size was subjected to milling to produce a suspension ofmicroparticles.

The suspension of calcium carbonate of relatively large particle sizewas prepared from a natural calcium carbonate, using the following:

For Experiment No. 12, illustrating the prior art, a sodiumpolyacrylate, partially neutralized (to the extent of 50%), having aweight average molecular weight Mw=6000 (by aqueous GPC), resulting fromradical polymerization of acrylic acid and corresponding to the materialfed to the separation apparatus, except that for the present test thematerial was neutralized to the extent of 100% with sodium hydroxide;

For Experiment No. 13, illustrating the invention, the sodiumpolyacrylate, partially neutralized (to the extent of 50%), ofExperiment No. 11, having a weight average molecular weight Mw=6070,except that for the present test the material was neutralized to theextent of 100% with sodium hydroxide after the separation.

For Experiments Nos. 12 and 13, the aqueous suspension of calciumcarbonate was prepared and milled with the same apparatus and under thesame operating conditions as in Experiments Nos. 4-7.

The experimental results are presented in Table 3.

                                      TABLE 3                                     __________________________________________________________________________             Milling Adjuvant Used                                                         Neutrali-                                                                             Atten-    Consumption                                                                         Brookfield Viscosity of the Suspension                zation  uatin in  of milling                                                                          (mPa-sec), at 20° C. and 76% dry                                       matter                                                for     second    adjuvant (%       8 days                                                                            8 days                                                                            8 days                   Experi-  Separation                                                                            inflection                                                                          Dry on dry    T.sub.0                                                                           8 days                                                                            AVAG                                                                              APAG,                                                                             APAG                     ment     (% and  peak of GPC                                                                         Matter                                                                            matter                                                                              T.sub.0 and                                                                       100 AVAG,                                                                             100 at 10                                                                             100                      No.      ion used)                                                                          Mw curve (%)                                                                           (%) basis)                                                                              10 rpm                                                                            T/min                                                                             10 rpm                                                                            T/min                                                                             rpm T/min                    __________________________________________________________________________    Prior Art                                                                          12  50 Na                                                                              6000                                                                             0     29  0.97  1760                                                                              660 25720                                                                             2370                                                                              10770                                                                             2600                     Invention                                                                          13  50 Na                                                                              6070                                                                             9.9   10.1                                                                              0.87   930                                                                              350 12930                                                                             2370                                                                               2070                                                                              670                     __________________________________________________________________________     AVAG: Measure of the viscosity prior to agitation of the suspension           APAG: Measure of the viscosity after agitation                           

It is seen from Table 3 that the separation, with the aid of a capillarymembrane, of the fractions of the polyacrylate, partially neutralized(to the extent of 50%) by sodium hydroxide, enables one to obtain amilling adjuvant or dispersing agent according to the invention, whichadjuvant or agent has a molecular weight distribution curve obtained byaqueous GPC with refractometric detection, wherein (in the curve) thesecond inflection peak, corresponding to a shoulder, has an attenuation,with respect to the initial product, of at least 9.9%.

It is also seen from Table 3 that the inventive milling adjuvant ordispersing agent according to the invention enables production of anaqueous suspension of calcium carbonate which is highly concentrated andis more stable than those according to prior art.

Example 4

In this Example, a milling adjuvant or dispersing agent according to theinvention was obtained by separation of a sodium polyacrylate partiallyneutralized (to the extent of 5%) by sodium hydroxide. The separationemployed a capillary membrane and was carried out at a temperaturevarying from 19 to 31° C. The product was then used as a millingadjuvant or dispersing agent.

Experiment No. 14:

An aqueous solution containing 26.3% of polyacrylate partiallyneutralized (to the extent of 5%) by sodium hydroxide, the abovepolyacrylate having a weight average molecular weight Mw=6000(determined by aqueous GPC), was diluted to 10% using water purified byreverse osmosis, and was then subjected to separation on the sameapparatus as in Experiment No. 1, under the conditions described below.

The same standards were used for the GPC determination as were used inExample 1.

After 2.5 hr of operation of the apparatus at a feed rate of 975 L/hrand a temperature which increased progressively from 19.3 to 30.8° C.,with entrance pressure which increased from 380 to 400 kPa, and exitpressure which increased from 80 to 110 kPa, the retentate,corresponding to a milling adjuvant or dispersing agent according to theinvention, was a sodium polyacrylate, partially neutralized (to theextent of 5%), having dry matter 10.9%, and a weight average molecularweight Mw=6050 (by aqueous GPC), and was characterized by a molecularweight distribution curve obtained by aqueous GPC with refractometricdetection, wherein (in the curve) the second inflection peak(corresponding to a shoulder) had an attenuation, with respect to theinitial product, of 3.5%; and the permeate was a sodium polyacrylate,partially neutralized (to the extent of 5%), having a weight averagemolecular weight Mw=2130 (by aqueous GPC), in water at a concentrationof 5.0% based on dry matter.

Experiment No. 15:

In this Experiment, which illustrates the invention, a suspension ofcalcium carbonate of relatively large particle size was subjected tomilling to produce a suspension of microparticles.

The suspension of calcium carbonate of relatively large particle sizewas prepared from a natural calcium carbonate, using the sodiumpolyacrylate, partially neutralized (to the extent of 5%), of ExperimentNo. 14, having a weight average molecular weight Mw=6050, except thatfor the present test the material was neutralized to the extent of 100%with sodium hydroxide after the separation.

For Experiment No. 15, the aqueous suspension of calcium carbonate wasprepared and milled with the same apparatus and under the same operatingconditions as in Experiments Nos. 4-7.

The experimental results are presented in Table 4.

                                      TABLE 4                                     __________________________________________________________________________             Milling Adjuvant Used                                                         Neutrali-                                                                             Atten-    Consumption                                                                         Brookfield Viscosity of the Suspension                zation  uatin in  of milling                                                                          (mPa-sec), at 20° C. and 76% dry                                       matter                                                for     second    adjuvant (%       8 days                                                                            8 days                                                                            8 days                   Experi-  Separation                                                                            inflection                                                                          Dry on dry    T.sub.0                                                                           8 days                                                                            AVAG                                                                              APAG,                                                                             APAG                     ment     (% and  peak of GPC                                                                         Matter                                                                            matter                                                                              T.sub.0 and                                                                       100 AVAG,                                                                             100 at 10                                                                             100                      No.      ion used)                                                                          Mw curve (%)                                                                           (%) basis)                                                                              10 rpm                                                                            T/min                                                                             10 rpm                                                                            T/min                                                                             rpm T/min                    __________________________________________________________________________    Invention                                                                          15  5 Na 6050                                                                             3.5   10.9                                                                              0.93  1300                                                                              470 21850                                                                             3590                                                                              5630                                                                              1650                     __________________________________________________________________________     AVAG: Measure of the viscosity prior to agitation of the suspension           APAG: Measure of the viscosity after agitation                           

It is seen from Table 4 that the separation, with the aid of a capillarymembrane, of the fractions of the polyacrylate, partially neutralized(to the extent of 5%) by sodium hydroxide, enables one to obtain amilling adjuvant or dispersing agent according to the invention whichadjuvant or agent has a molecular weight distribution curve obtained byaqueous GPC with refractometric detection, wherein (in the curve) thesecond inflection peak, corresponding to a shoulder, has an attenuation,with respect to the initial product, of at least 3.5%.

It is also seen from Table 4 that the milling adjuvant or dispersingagent according to the invention enables production of an aqueoussuspension of calcium carbonate which is highly concentrated, whereas noprior art method of separation enables production, at 5% neutralization,of a milling adjuvant or dispersing agent.

Example 5

In this Example, a milling adjuvant or dispersing agent according to theinvention was obtained by separation of a polyacrylic acid, with the aidof a capillary membrane, at a temperature varying from 20.2 to 32.8° C.The product was then used as a milling adjuvant or dispersing agent.

Experiment No. 16:

An aqueous solution containing 24.7% of polyacrylic acid, having aweight average molecular weight Mw=4500 (determined by aqueous GPC), wasdiluted to 15% with water, and was then subjected to separation on thesame apparatus as in Experiment No. 1, under the conditions describedbelow.

The same standards were used for the GPC determination as were used inExample 1.

After 22 hr of operation of the apparatus at a feed rate of 1200 L/hrand a temperature which varied from 20.2 to 32.8° C., with entrancepressure which increased from 150 to 320 kPa and exit pressure whichincreased from 50 to 160 kPa, the retentate, corresponding to a millingadjuvant or dispersing agent according to the invention, was apolyacrylic acid having a weight average molecular weight Mw=4600 (byaqueous GPC), in water at a concentration of 17.5% based on dry matter,and was characterized by a molecular weight distribution curve obtainedby aqueous GPC with refractometric detection, wherein (in the curve) thesecond inflection peak (corresponding to a shoulder) had an attenuation,with respect to the initial product, of 8.2%; and the permeate was apolyacrylic acid having a weight average molecular weight Mw=2200 (byaqueous GPC), in water at a concentration of 6.0% based on dry matter.

Experiments Nos. 17 (comparative) and 18:

In these Experiments, a suspension of calcium carbonate of relativelylarge particle size was subjected to milling to produce a suspension ofmicroparticles.

The suspension of calcium carbonate of relatively large particle sizewas prepared from a natural calcium carbonate, using the following:

For Experiment No. 17, illustrating the prior art, a polyacrylic acidhaving a weight average molecular weight Mw=4500 (by aqueous GPC),resulting from radical polymerization of acrylic acid and correspondingto the material fed to the separation apparatus, except that for thepresent test the material was neutralized to the extent of 100% withsodium hydroxide;

For Experiment No. 18, illustrating the invention, the polyacrylic acidof Experiment No. 16, having a weight average molecular weight Mw=4600,except that for the present test the material was neutralized to theextent of 100% with sodium hydroxide after the separation.

For Experiments Nos. 17 and 18, the aqueous suspension of calciumcarbonate was prepared and milled with the same apparatus and under thesame operating conditions as in Experiments Nos. 4-7.

The experimental results are presented in Table 5.

                                      TABLE 5                                     __________________________________________________________________________             Milling Adjuvant Used                                                         Neutrali-                                                                             Atten-    Consumption                                                                         Brookfield Viscosity of the Suspension                zation  uatin in  of milling                                                                          (mPa-sec), at 20° C. and 76% dry                                       matter                                                for     second    adjuvant (%       8 days                                                                            8 days                                                                            8 days                   Experi-  Separation                                                                            inflection                                                                          Dry on dry    T.sub.0                                                                           8 days                                                                            AVAG                                                                              APAG,                                                                             APAG                     ment     (% and  peak of GPC                                                                         Matter                                                                            matter                                                                              T.sub.0 and                                                                       100 AVAG,                                                                             100 at 10                                                                             100                      No.      ion used)                                                                          Mw curve (%)                                                                           (%) basis)                                                                              10 rpm                                                                            T/min                                                                             10 rpm                                                                            T/min                                                                             rpm T/min                    __________________________________________________________________________    Prior Art                                                                          17  0    4500                                                                             0     24.7%                                                                             1.08  1400                                                                              400 2030                                                                              650 1120                                                                              330                      Invention                                                                          18  0    4600                                                                             8.2   17.5%                                                                             1.08  1400                                                                              400 1900                                                                              640 850 280                      __________________________________________________________________________     AVAG: Measure of the viscosity prior to agitation of the suspension           APAG: Measure of the viscosity after agitation                           

It is seen from Table 5 that the separation, with the aid of a capillarymembrane, of the fractions of the polyacrylic acid enables one to obtaina milling adjuvant or dispersing agent according to the invention whichadjuvant or agent has a molecular weight distribution curve obtained byaqueous GPC with refractometric detection, wherein (in said curve) thesecond inflection peak, corresponding to a shoulder, has an attenuation,with respect to the initial product, of at least 8.2%.

It is also seen from Table 5 that the milling adjuvant or dispersingagent according to the invention enables production of an aqueoussuspension of calcium carbonate which is at least as stable assuspensions produced with non-separated products according to the stateof the art; further, that no prior art method of separation enablesproduction of a milling adjuvant or dispersing agent in a completelyacid state.

Example 6

A milling adjuvant or dispersing agent according to the invention wasobtained by separation of a sodium polyacrylate completely neutralizedby sodium hydroxide. The separation employed a system of a plurality ofnanofiltration membranes of flat or tubular configuration, mounted inseries, and was carried out at about 68° C. The product was then used asa milling adjuvant or dispersing agent.

Experiment No. 19:

An aqueous solution containing 24.50% of sodium polyacrylate, whichpolyacrylate had been completely neutralized with sodium hydroxide andhad a weight average molecular weight Mw=5160 (determined by aqueousGPC) was fed at 400 L/hr, by means of a "Moineau" circulating pump, tothe system of membranes firmly mounted on a carbon support, whichmembranes had been surface-treated by quaternized polyethylene imine.The surface area of the membranes was 0.0113 sq m.

The same standards were used for the GPC determination as were used inExample 1.

After 7 hr 30 min of operation of the apparatus at 68° C. and a pressureof 3000 kPa, the retentate, corresponding to a milling adjuvant ordispersing agent according to the invention, was a completelyneutralized sodium polyacrylate having a weight average molecular weightMw=5520 (by aqueous GPC), in water at a concentration of 22% based ondry matter, and was characterized by a molecular weight distributioncurve obtained by aqueous GPC with refractometric detection, wherein (inthe curve) the second inflection peak, corresponding to a shoulder, hadan attenuation, with respect to the initial product, of at least 15.0%;and the permeate was a completely neutralized sodium polyacrylate havinga weight average molecular weight Mw=2430 (by aqueous GPC), in water ata concentration of 6.5% based on dry matter.

Experiments Nos. 20 (comparative) and 21:

In these Experiments, a suspension of calcium carbonate of relativelylarge particle size was subjected to milling to produce a suspension ofmicroparticles.

The suspension of the coarse material was prepared from a naturalcalcium carbonate, using the following:

For Experiment No. 20, illustrating the prior art, a completelyneutralized sodium polyacrylate of a weight average molecular weightMw=5160 (by aqueous GPC), resulting from radical polymerization ofacrylic acid, and corresponding to the product fed to the separatingapparatus;

For Experiment No. 21, illustrating the invention, the completelyneutralized sodium polyacrylate from Experiment No. 19, having Mw=5520.

For Experiments Nos. 20 and 21, the aqueous suspension of calciumcarbonate was prepared and milled with the same apparatus and under thesame operating conditions as in Experiments Nos. 4-7.

The experimental results are presented in Table 6.

                                      TABLE 6                                     __________________________________________________________________________             Milling Adjuvant Used                                                         Neutrali-                                                                             Atten-    Consumption                                                                         Brookfield Viscosity of the Suspension                zation  uatin in  of milling                                                                          (mPa-sec), at 20° C. and 76% dry                                       matter                                                for     second    adjuvant (%       8 days                                                                            8 days                                                                            8 days                   Experi-  Separation                                                                            inflection                                                                          Dry on dry    T.sub.0                                                                           8 days                                                                            AVAG                                                                              APAG,                                                                             APAG                     ment     (% and  peak of GPC                                                                         Matter                                                                            matter                                                                              T.sub.0 and                                                                       100 AVAG,                                                                             100 at 10                                                                             100                      No.      ion used)                                                                          Mw curve (%)                                                                           (%) basis)                                                                              10 rpm                                                                            T/min                                                                             10 rpm                                                                            T/min                                                                             rpm T/min                    __________________________________________________________________________    Prior Art                                                                          20  100 Na                                                                             5160                                                                             0     24.5                                                                              0.97  1275                                                                              500 40000                                                                             5000                                                                              7100                                                                              2050                     Invention                                                                          21  100 Na                                                                             5520                                                                             15.0  22  0.9   1050                                                                              380  3200                                                                             2620                                                                              1350                                                                               500                     __________________________________________________________________________     AVAG: Measure of the viscosity prior to agitation of the suspension           APAG: Measure of the viscosity after agitation                           

It is seen from Table 6 that the separation--with the aid of a system ofmembranes on a carbon support, which are surface-treated withpolyethylene imine--of the fractions of the polyacrylate, completelyneutralized by sodium hydroxide, enables one to obtain a millingadjuvant or dispersing agent according to the invention which adjuvantor agent has a molecular weight distribution curve obtained by aqueousGPC with refractometric detection, wherein (in the curve) the secondinflection peak, corresponding to a shoulder, has an attenuation, withrespect to the initial product, of at least 15.0%.

It is also seen from Table 6 that the inventive milling adjuvant ordispersing agent according to the invention enables production of anaqueous suspension of calcium carbonate which are highly concentratedand are more stable than those obtained with a non-separated millingadjuvant according to the prior art.

Example 7

A milling adjuvant or dispersing agent according to the invention wasobtained by separation, with a "Carbosep® M5" membrane based on carbonand zirconium, of a copolymer completely neutralized by sodiumhydroxide. The separation was carried out at a temperature in the orderof 25° C. The product was then used as a milling adjuvant or dispersingagent.

Experiment No. 22:

An aqueous solution containing 30% of copolymer based on dry matter,which copolymer had been completely neutralized with sodium hydroxide,was comprised of 97 wt. % of acrylic acid monomer (based on the totalweight of monomers) and 3 wt. % of acrylamidomethylpropanesulfonic acid(AMPS) (based on the total weight of monomers), had a weight averagemolecular weight Mw=4700 (determined by aqueous GPC), and had beendiluted to 2% by water purified by reverse osmosis, was introduced tothe separating apparatus at a feed rate of 8 L/hr per sq m of membrane,at a temperature of 25° C. and pressure 100 kPa.

The retentate obtained, corresponding to a milling adjuvant ordispersing agent according to the invention, was a completelyneutralized copolymer of acrylic acid and AMPS, having a weight averagemolecular weight Mw=4950 (by aqueous GPC), in water at a concentrationof 1.6% based on dry matter, and was characterized by a molecular weightdistribution curve obtained by aqueous GPC with refractometricdetection, wherein (in the curve) the second inflection peak had anattenuation, with respect to the initial product, of 6.0%; and thepermeate was a completely neutralized copolymer of acrylic acid andAMPS, having a weight average molecular weight Mw=1000 (by aqueous GPC),in water at a concentration of 0.6% based on dry matter.

Experiments Nos. 23 (comparison) and 24:

In these Experiments, a suspension of calcium carbonate of relativelylarge particle size was subjected to milling to produce a suspension ofmicroparticles.

The suspension of the coarse material was prepared from a naturalcalcium carbonate, using the following:

For Experiment No. 23, illustrating the prior art, a completelyneutralized copolymer of acrylic acid and AMPS, of a weight averagemolecular weight Mw=4700 (by aqueous GPC), in a water at a concentrationof 30% based on dry matter, the above copolymer resulting from radicalcopolymerization of acrylic acid and AMPS, and corresponding to theproduct fed to the separating apparatus;

For Experiment No. 24, illustrating the invention, the copolymer fromExperiment No. 22, completely neutralized by sodium hydroxide.

For Experiments Nos. 23 and 24, the aqueous suspension of calciumcarbonate was prepared and milled with the same apparatus and under thesame operating conditions as in Experiments Nos. 4-7.

The experimental results are presented in Table 7.

                                      TABLE 7                                     __________________________________________________________________________             Milling Adjuvant Used                                                         Neutrali-                                                                             Atten-    Consumption                                                                         Brookfield Viscosity of the Suspension                zation  uatin in  of milling                                                                          (mPa-sec), at 20° C. and 76% dry                                       matter                                                for     second    adjuvant (%       8 days                                                                            8 days                                                                            8 days                   Experi-  Separation                                                                            inflection                                                                          Dry on dry    T.sub.0                                                                           8 days                                                                            AVAG                                                                              APAG,                                                                             APAG                     ment     (% and  peak of GPC                                                                         Matter                                                                            matter                                                                              T.sub.0 and                                                                       100 AVAG,                                                                             100 at 10                                                                             100                      No.      ion used)                                                                          Mw curve (%)                                                                           (%) basis)                                                                              10 rpm                                                                            T/min                                                                             10 rpm                                                                            T/min                                                                             rpm T/min                    __________________________________________________________________________    Prior Art                                                                          23  100 Na                                                                             4700                                                                             0     30  0.98  3720                                                                              980 47000                                                                             6460                                                                              19580                                                                             4700                     Invention                                                                          24  100 Na                                                                             4950                                                                             6.0   1.6 0.93  1200                                                                              350 15000                                                                             2200                                                                               9800                                                                             2350                     __________________________________________________________________________     AVAG: Measure of the viscosity prior to agitation of the suspension           APAG: Measure of the viscosity after agitation                           

It is seen from Table 7 that the separation, with the aid of a Carbosep®M5 membrane, of the fractions of the copolymer of acrylic acid and AMPS,which has been completely neutralized by sodium hydroxide, enables oneto obtain a milling adjuvant or dispersing agent according to theinvention which adjuvant or agent has a molecular weight distributioncurve obtained by aqueous GPC with refractometric detection, wherein (inthe curve) the second inflection peak, corresponding to a shoulder, hasan attenuation, with respect to the initial product, of at least 6%.

It is also seen from Table 7 that the milling adjuvant or dispersingagent according to the invention enables production of an aqueoussuspension of calcium carbonate which is highly concentrated and is morestable than those according to the prior art.

Example 8

A milling adjuvant or dispersing agent according to the invention wasobtained by separation, with the aid of the membrane employed in Example7, of a polymer completely neutralized by a mixture of sodium hydroxideand magnesium hydroxide. The separation was carried out at a temperaturein the order of 25° C. The product was then used as a milling adjuvantor dispersing agent.

Experiment No. 25:

An aqueous solution containing 31% of a polyacrylate based on drymatter, which had been completely neutralized with a mixture comprisedof 60% sodium hydroxide and 40% magnesium hydroxide, had a weightaverage molecular weight Mw=5160 (determined by aqueous GPC), and hadbeen diluted to 2% by water purified by reverse osmosis, was subjectedto separation of fractions, using the same equipment and operatingconditions as in Experiment No. 22.

The retentate obtained, corresponding to a milling adjuvant ordispersing agent according to the invention, was a polyacrylatecompletely neutralized by a mixture of sodium hydroxide and magnesiumhydroxide, which polyacrylate had a weight average molecular weightMw=5400 (by aqueous GPC), in water at a concentration of 1.6% based ondry matter, and was characterized by a molecular weight distributioncurve obtained by aqueous GPC with refractometric detection, wherein (inthe curve) the second inflection peak had an attenuation, with respectto the initial product, of 6.0%; and the permeate was a polyacrylatecompletely neutralized by a mixture of sodium hydroxide and magnesiumhydroxide, which polyacrylate had a weight average molecular weightMw=2000 (by aqueous GPC), in water at a concentration of 0.6% based ondry matter.

Experiments Nos. 26 comparison and 27:

In these Experiments, a suspension of calcium carbonate of relativelylarge particle size was subjected to milling to produce a suspension ofmicroparticles.

The suspension of the coarse material was prepared from a naturalcalcium carbonate, using the following:

For Experiment No. 26, illustrating the prior art, a polyacrylate whichhad been completely neutralized with a mixture comprised of 60% sodiumhydroxide and 40% magnesium hydroxide, had a weight average molecularweight Mw=5160 (determined by aqueous GPC), in water at a concentrationof 31.0% based on dry matter, the above polyacrylate resulting fromradical polymerization of acrylic acid, and corresponding to the productfed to the separating apparatus;

For Experiment No. 27, illustrating the invention, the polyacrylate fromExperiment No. 25.

For Experiments Nos. 26 and 27, the aqueous suspension of calciumcarbonate was prepared and milled with the same apparatus and under thesame operating conditions as in Experiments Nos. 4-7.

The experimental results are presented in Table 8.

                                      TABLE 8                                     __________________________________________________________________________             Milling Adjuvant Used                                                         Neutrali-                                                                              Atten-    Consumption                                                                         Brookfield Viscosity of the Suspension               zation   uatin in  of milling                                                                          (mPa-sec), at 20° C. and 76% dry                                       matter                                               for      second    adjuvant (%       8 days                                                                            8 days                                                                            8 days                  Experi-  Separation                                                                             inflection                                                                          Dry on dry    T.sub.0                                                                           8 days                                                                            AVAG                                                                              APAG,                                                                             APAG                    ment     (% and   peak of GPC                                                                         Matter                                                                            matter                                                                              T.sub.0 and                                                                       100 AVAG,                                                                             100 at 10                                                                             100                     No.      ion used)                                                                           Mw curve (%)                                                                           (%) basis)                                                                              10 rpm                                                                            T/min                                                                             10 rpm                                                                            T/min                                                                             rpm T/min                   __________________________________________________________________________    Prior Art                                                                          26  60 Na/40 Mg                                                                         5160                                                                             0     31.0                                                                              1.15  1500                                                                              480 3400                                                                              880 1300                                                                              380                     Invention                                                                          27  60 Na/40 Mg                                                                         5400                                                                             6.0   1.6 1.11  1350                                                                              400 2000                                                                              580 1030                                                                              290                     __________________________________________________________________________     AVAG: Measure of the viscosity prior to agitation of the suspension           APAG: Measure of the viscosity after agitation                           

It is seen from Table 8 that the separation, with the aid of a Carbosep®M5 membrane, of the fractions of the polyacrylate which polyacrylate hasbeen completely neutralized by a mixture of sodium hydroxide andmagnesium hydroxide, enables one to obtain a milling adjuvant ordispersing agent according to the invention which adjuvant or agent hasa molecular weight distribution curve obtained by aqueous GPC withrefractometric detection, wherein (in the curve) the second inflectionpeak, corresponding to a shoulder, has an attenuation, with respect tothe initial product, of at least 6.0%.

It is also seen from Table 8 that the milling adjuvant or dispersingagent according to the invention enables production of an aqueoussuspension of calcium carbonate which is highly is concentrated and ismore stable than those according to the prior art.

Although the present invention has been described with reference tospecific details of certain embodiments thereof, it is not intended thatsuch details should be regarded as limitations upon the scope of theinvention except insofar as they are included in the accompanyingclaims.

Example 9

This example relates to the obtaining of a milling adjuvant ordispersing agent in accordance with the invention by separation with theaid of a capillary membrane, at a temperature ranging from 20° C. to 33°C., of an acrylic and methacrylamide acid copolymer 50% partiallyneutralized by soda, as well as its use as a milling adjuvant ordispersing agent.

Test No. 28:

For this purpose, an aqueous solution with 29.4% dry-matterconcentration of an acrylic and methacrylamide acid copolymer 50%partially neutralized by soda, of a weight average molecular weightMw=5350 determined by aqueous GPC, was diluted 10% with water purifiedby reverse osmosis then separated with the same apparatus as that fortest No. 1 and under the conditions described below.

For the GPC measurements, the same standards as those for example 1 areapplied.

After 7 hours of operation of the device at a feed rate ranging from 700to 1200 l/h with a temperature gradually increasing from 20.6° C. to33.5° C. and a pressure at intake on the order of 2,5.10⁵ Pa and atoutlet on the order of 1,3.10⁵ Pa, the retained material collected,corresponding to the milling adjuvant or dispersing agent according tothe invention, is an acrylic-methacrylamide acid copolymer 50% partiallyneutralized by soda having a dry-matter content of 10.0%, a weightaverage molecular weight Mw=6100 determined by aqueous GPC and ischaracterized by a molecular-weight distribution curve obtained byaqueous GPC and refractometric detection showing a decrease of 6.8% withrespect to the initial product, in the second curvature peakcorresponding to a shoulder when the permeate is a 50%partially-neutralized copolymer having a dry-matter content of 7.6% anda weight average molecular weight Mw=2900 determined by aqueous GPC.

Test No. 29 and No. 30:

These tests relate to the preparation of a coarse calcium carbonatesuspension subjected to a milling in order to refine it to amicroparticulate suspension.

For this purpose, a coarse calcium carbonate suspension was preparedfrom a natural calcium carbonate by making use of:

for test No. 29 illustrating the prior art, an acrylic-methacrylamideacid copolymer with a weight average molecular weight Mw=5350 determinedby aqueous GPC and corresponding to the feed product for the separationdevice of test No. 28 but 100% neutralized with soda for said test.

for test No. 30 illustrating the invention, the 50%partially-neutralized acrylic-methacrylic acid of test No. 28 and withMw=6100 but also 100% neutralized for said test with soda afterseparation.

For each test, the preparation of the aqueous calcium carbonatesuspension and its crushing were performed under the same operatingconditions and with the same apparatus as for tests No. 4 to 7.

The experimental results are collected in table 9 below:

                                      TABLE 9                                     __________________________________________________________________________                                     Brookfield Viscosity of the Suspension                Milling Adjuvant Used   (at 20° C. in M.Pa.s) with 76%                                         dry matter                                            Neutrali-                                                                             Attenuation                                                                             Agent         8 days                                                                            8 days                                                                            8 days                                                                            8 days                   Experi-  zation for                                                                            in second                                                                           Dry consumption                                                                             T.sub.0                                                                           AVAG,                                                                             AVAG                                                                              APAG,                                                                             APAG                     ment     Separation                                                                            inflection                                                                          extract                                                                           in    T.sub.0 10                                                                        100 10  100 10  100                      No.      (in %)                                                                             Mw (%)   %   dry/dry                                                                             T/min                                                                             T/min                                                                             T/min                                                                             T/min                                                                             T/min                                                                             T/min                    __________________________________________________________________________    Prior Art                                                                          29  50 Na                                                                              5350                                                                             --    29.4                                                                              0.99  2090                                                                              800 17500                                                                             3200                                                                              3480                                                                              1350                     Invention                                                                          30  50 Na                                                                              6100                                                                             6.8   10.0                                                                              0.95  1450                                                                              540 11250                                                                             2600                                                                              2000                                                                               760                     __________________________________________________________________________     AVAG: Measure of the viscosity prior to agitation of the suspension           APAG: Measure of the viscosity after agitation of the suspension         

Reading of table 9 allows us to state that fractionation, with the aidof a capillary membrane, of an acrylic-methacrylamide acid 50% partiallyneutralized by soda makes it possible to obtain a milling adjuvant ordispersing agent in accordance with the invention for which themolecular-weight distribution curve obtained by aqueous GPC analysis andrefractometric detection shows a decrease in the second curvature peak,corresponding to a shoulder, of at least 6.8% with respect to theinitial product.

This reading also allows us to state that the milling or dispersingagent in accordance with the invention makes it possible to achievehighly concentrated aqueous suspensions of calcium carbonate more stablethan those obtained with the unseparated milling agent of the prior art.

Example 10

This example relates to the obtaining of a dispersing agent inaccordance with the invention by the separation, with the aid of acapillary membrane at a temperature ranging from 26° C. to 39° C., of anacrylic and maleic anhydride acid completely neutralized by soda as wellas its use as a dispersing agent.

Test No. 31:

For this purpose an aqueous solution with 35.3% dry-matter concentrationof an acrylic-maleic anhydride acid completely neutralized by soda, witha weight average molecular weight Mw=19800 determined by aqueous GPC,has been diluted 10% with water purified by reverse osmosis, thenseparated with the same apparatus as that for test No. 1 and under theconditions described below.

For the GPC measurements, the same standards as those for example 1 areapplied.

After 7 hours of operation of the device at a feed flow ranging from 700to 1200 l/h with a temperature gradually increasing from 26.6° C. to39.2° C. and a pressure at intake on the order of 3,4.10⁵ Pa to 3,7. 10⁵Pa and at outlet 1,0.10⁵ Pa to 1,1.10⁵ Pa, the retained materialcollected corresponding to the dispersing agent in accordance with theinvention is an acrylic-maleic anhydride acid copolymer completelyneutralized by soda having a dry-matter content of 11.7%, a weightaverage molecular weight Mw=21900 determined by aqueous GPC and ischaracterized by a molecular-weight distribution curve obtained byaqueous GPC analysis and refractometric detection showing a decrease of3.4% with respect to the initial product, in the second curvature peakcorresponding to a shoulder when the permeate is an acrylic-maleicanhydride acid completely neutralized by soda having a dry-mattercontent of 4.0% and a weight average molecular weight Mw=3900 determinedby aqueous GPC.

Tests No. 32 and 33:

These tests relate to the preparation of a calcium carbonate suspensionby dispersion of said carbonate in water by making use, for test No. 32,of the acrylic-maleic anhydride acid copolymer completely neutralized bysoda and with Mw=19800 corresponding to the feed product for theseparation device of test No. 31 to illustrate the prior art and bymaking use, for test No. 33, illustrating the invention, of thecompletely neutralized copolymer of test No. 31 and with Mw=21900.

For this purpose, for test No. 32 illustrating the prior art, there wasintroduced under agitation in a vessel with a capacity of 1.5 liters andequipped with an agitator disk 50 mm in diameter, 322 grams of water and17.0 grams of acrylic-maleic anhydride acid completely neutralized bysoda and with a dry-matter concentration of 35.3%. There then was addedslowly and under agitation on the order of 1000 revolutions/minute, 1000grams of Norwegian marble with granulometry determined by a Sedigraph5100 from the Micromeritics company and the equivalent of 75% of theparticles sized below 1 micrometer.

After the addition is completed, the agitation is brought up to 8000revolutions/minute for 10 minutes. At the conclusion of these 10minutes, the viscosity of the suspension is measured with the aid of aBrookfield RVT-type viscometer at a temperature of 20° C. and a rotationspeed of 100 rpm for the No. 3 spindle.

After a settling time of 7 days for the suspension, the viscosity of thesuspension is measured by insertion of the No. 3 spindle of theBrookfield RVT-type viscometer into the unagitated vessel at atemperature of 20° C. and a rotation speed of 100 rpm (viscosityAVAG=prior to agitation). The same viscosity measurement is performedonce the vessel is agitated and constitutes the result of the viscosityAGAG (after agitation).

For test No. 33 illustrating the invention, there was prepared, with thesame apparatus and under the same conditions as for the preceding test,a suspension of Norwegian marble by the use of 288 grams of water, 51.3grams of the acrylic-maleic anhydride acid copolymer of test No. 31 withMw=21900 and a dry-matter concentration of 11.7w and finally 1000 gramsof the same Norwegian marble as that for the preceding test. Theviscosity measurements were performed with the same operating mode andthe same apparatus as those for the preceding test.

The results of these measurements are collected in table 10 below:

                                      TABLE 10                                    __________________________________________________________________________                                      Brookfield Viscosity of the Suspension               Milling Adjuvant Used    (at 20° C. in M.Pa.s) with 75%                                         dry matter                                           Neutrali-                                                                              Attenuation                                                                             Agent       7 days                                                                              7 days                          Experi-  zation for                                                                             in second                                                                           Dry consumption                                                                         To    AVAG  APAG                            ment     Separation                                                                             inflection                                                                          extract                                                                           in    100   100   100                             No.      (in %)                                                                             Mw  (%)   %   dry/dry                                                                             T/min T/min T/min                           __________________________________________________________________________    Prior Art                                                                          32  100 Na                                                                             19800                                                                             --    35.3                                                                              0.6   300   1750  270                             Invention                                                                          33  100 Na                                                                             21900                                                                             3.4   11.7                                                                              0.6   235    850  260                             __________________________________________________________________________     AVAG: Measure of the viscosity prior to agitation of the suspension           APAG: Measure of the viscosity after agitation of the suspension         

Reading of table 10 allows us to state that fractionation, with the aidof a capillary membrane, of an acrylic-maleic anhydride acid copolymercompletely neutralized by soda makes it possible to obtain a dispersingagent in accordance with the invention in which the molecular-weightdistribution curve obtained by aqueous GPC analysis and refractometricdetection shows a decrease in the second curvature peak, correspondingto a shoulder, of at least 3.4% with respect to the initial product.

This reading also allows us to state that the dispersing agent inaccordance with the invention makes it possible to achievehighly-concentrated aqueous calcium carbonate suspensions more stablethan those of the prior art.

What is claimed as new and is desired to be secured by Letters Patentsof the United States is:
 1. A milling adjuvant or dispersing agent,produced by a process, comprising:a) introducing a water-solubleseparand material in an aqueous medium into a separation apparatushaving one or more organic or mineral membranes, said one or moremembranes being optionally borne on a support; and b) separating thewater-soluble separand material into a plurality of permeate andretentate phases containing different molecular weight fractions of saidseparand material by differences therebetween in hydrodynamic volume ina continuous or batch process; wherein at least one of said phases is aretentate phase and contains said milling adjuvant or dispersing agent;wherein said water-soluble separand material is selected from the groupconsisting of a vinyl polymer, vinyl copolymer, acrylic polymer, acryliccopolymer, polycondensate polymer and polycondensate copolymer; whereinsaid water-soluble separand material has at least one acidic functionalgroup; further wherein said milling adjuvant or dispersing agentobtained exhibits a molecular weight distribution curve obtained byaqueous gel permeation chromatography with refractometric detection,wherein a second inflection peak in said curve, corresponding to ashoulder, has an of attenuation of least 3% based on the introducedwater-soluble separand material, irrespective of a dry matter content ofthe water-soluble separand material introduced into the separationapparatus; and wherein said acidic functional group of saidwater-soluble separand material is partially-, fully neutralized orunneutralized.
 2. The milling adjuvant or dispersing agent according toclaim 1, which contains said water-soluble separand material in anamount of 1.5 to 50% based upon total dry matter.
 3. The millingadjuvant or dispersing agent according to claim 1, which is producedwithout using organic solvent.
 4. The milling adjuvant or dispersingagent according to claim 1, wherein said amine is aliphatic or cyclic,and primary, secondary or tertiary.
 5. The milling adjuvant ordispersing agent according to claim 1, which is in the form of asolution.
 6. The milling adjuvant or dispersing agent according to claim1, which is in the form of a powder.
 7. The milling adjuvant ordispersing agent according to claim 1, wherein said aqueous medium ofstep a) contains no organic solvent.
 8. The milling adjuvant ordispersing agent according to claim 1, wherein said acidic functionalgroup of said water-soluble separand material is unneutralized.
 9. Themilling adjuvant or dispersing agent according to claim 1, wherein saidwater-soluble separand material is partially- or fully neutralized. 10.An aqueous mineral suspension for pigments, comprising a compositionproduced by a process, comprising:a) introducing a water-solubleseparand material in an aqueous medium into a separation apparatushaving one or more organic or mineral membranes, said one or moremembranes being optionally borne on a support; and b) separating thewater-soluble separand material into a plurality of permeate andretentate phases containing different molecular weight fractions of saidseparand material by differences therebetween in hydrodynamic volume ina continuous or batch process; wherein at least one of said phases is aretentate phase and contains said milling adjuvant or dispersing agent;wherein said water-soluble separand material is selected from the groupconsisting of a vinyl polymer, vinyl copolymer, acrylic polymer, acryliccopolymer, polycondensate polymer and polycondensate copolymer; whereinsaid water-soluble separand material has at least one acidic functionalgroup; further wherein said composition obtained exhibits a molecularweight distribution curve obtained by aqueous gel permeationchromatography with refractometric detection, wherein a secondinflection peak in said curve, corresponding to a shoulder, has anattenuation of at least 3% based on the introduced water-solubleseparand material, irrespective of a dry matter content of thewater-soluble separand material introduced into the separationapparatus; and wherein said acidic functional group of saidwater-soluble separand material is partially-, fully neutralized orunneutralized.
 11. The aqueous mineral suspension according to claim 10,wherein said composition contains said water-soluble separand materialin an amount of 1.5 to 50% based upon total dry matter.
 12. The aqueousmineral suspension according to claim 10, wherein said composition isproduced without using organic solvent.
 13. The aqueous mineralsuspension according to claim 10, which comprises 0.05 to 2% of saidmilling adjuvant or dispersing agent.
 14. The aqueous mineral suspensionaccording to claim 10, wherein said aqueous medium of step a) containsno organic solvent.
 15. The aqueous mineral suspension according toclaim 10, wherein said acidic functional group of said water-solubleseparand material is partially- or fully neutralized.
 16. The aqueousmineral suspension according to claim 10, wherein said acidic functionalgroup of said water-soluble separand material is unneutralized.